Container having metal walls and/or shell and bottom, particularly aerosol cans having a decoration, are formed either of one part or of several parts. In the case of one-piece aerosol cans of aluminum, the cylindrical can body is provided by cold sinking. Subsequently, a valve seat is formed at the open end by means of an upset necking procedure. This process of production is very expensive due to the installation required for the bulk of treatment steps as well as for the requirements regarding water and energy for cleaning and drying. U.S. Pat. No. 4,095,544 and EP-0 666 124 A1 describe the production of seamless steel cans. There, a cylindrical can body is manufactured from a steel sheet coated with tin or plastic material by punching, pressing and ironing. It turned out that enormous problems occur with forming restricted neck portions, because the material's structure is changed and hardened by ironing. Very current are also cans of steel sheet where the shell has a longitudinal welding seam. The bottom and the upper closure are fastened to the shell by folded seam connections. With folded seam connections sealing problems may occur which, for example, are reduced by sealing rings. Problems result also in the current extremely thin-walled cans with sealings that are arranged on the end face. From documents EP 200 098 A2 and EP 208 564, two-piece or multipart cans are known where the parts are interconnected by laser welding. The shape of the cans given by the known laser welding seams in the interconnection zones between the can's wall and the bottom or valve seat are not attractive and, moreover, a cost-effective production of sufficiently high piece numbers per time unit cannot be achieved with the known process. The above-mentioned longitudinal welding seams, particularly the longitudinal welding seams known from U.S. Pat. No. 4,341,943 too, have small steps or differences in thickness in peripheral direction which lead to problems at the can body when necking the neck portion, and to an elevated load of the necking tools.
From WO 02/02257 A1, a process for forming a neck portion is known where a deforming surface cooperates with a propping surface in such a manner that the can's wall is deformed between these two surfaces under tensile forces. In doing this, the deforming surface is moved inwards in radial direction, while the can's wall is always in contact to the propping surface that engages the radial inner side. It has turned out that the gap region between the two surfaces, which engage both sides of the can's wall, have to be precisely adapted to the wall thickness which is variable in this region, and that the tensile forces in the can's wall have to be continuously chosen in such a way that necking does not result in a bulb. In the case of a bulb, the forces acting through the two surfaces onto the can's wall would become locally very high which entrains the risk of damaging. It has turned out that keeping the appropriate conditions when necking by cooperating deforming and propping surfaces is very difficult.
Apart from a restricted neck portion, narrowing is also desired at the transition to the bottom surface of current can bodies. Since mostly the bottom has already been inserted when forming the neck portion, narrowing the bottom region is suitably done previously which, however, is difficult with a can shell having no upper or lower closure.
For esthetic reasons and to mark its contents, a decoration is applied at the outside of the shell surface. In order to be able to do without expensively and inflexibly printing the can body, printed films are applied onto the can body. According to EP 0 525 729, a decorating film is directly wound in peripheral direction onto the can body, and is connected to form a closed film envelope on the can body. Separating a piece of film is very difficult with thin films. To interconnect the film ends by a seal connection, a seal surface is pressed against the can body which is, however, not quite convenient with thin-walled cans due to their small stability. With cans whose outer surfaces are restricted at the lower, and particularly at the upper can end and which deviate from a cylindrical surface, forming a non-wavy seal connection over the whole can height is not possible.
Solutions are known from documents U.S. Pat. No. 4,199,851, DE 197 16 079 and EP 1 153 837 A1 where a shrinkable flat plastic material is wound around a coil mandrel to form a closed envelope, is shifted in axial direction as an all-around label onto a bottle or a can, and is then shrunk-fixed. Shifting the all-around label over a bottle or a can without jamming involves various problems, particularly with thin films. With the thin decorating films mentioned in EP 1 153 837 A1, having a thickness of less than 25 μm, preferably between 9 μm and 21 μm, the risk of deforming or damaging is very high when shifting the closed film envelops from the coil mandrel onto the can body. The printable commercial plastic film Label-Lyte ROSO LR 400 of the Mobil Oil Corporation comprises a thin seal layer on both sides and is available with a thickness of 20 μm and of 50 μm. When sealing the overlapping zone the sealing layer which engages the coil mandrel is also heated and pressed against the coil mandrel. The film has now different sliding properties in the region of the seal strip. Further problems may occur through friction dependent electrostatic loads and the involved forces which act onto the film. Transferring a cylindrical closed film from a coil mandrel to a can body is problematic even if the diameter of the coil mandrel is a little bit larger than the diameter of the can body. A clear difference in size is not desirable, because in this case the ability of shrinking of the film has to be larger, and there is the risk that undulations form under fix-shrinking. In addition, for raising the ability of shrinking a film of a greater thickness had to be used which is not desirable. A further problem consists in that thin films can be separated only at large expenses. Due to the difficulty of separating alone, solutions are not desired where film pieces are wound around a coil mandrel or around a can body.
The known approaches for producing cans use expensive installations, and their operation is dependent upon a specialized personnel. Therefore, the cans cannot be produced at the filling factories. Thus, much transport expenses will occur to transport empty cans from the can producer to the filling factories.